Electric heating element



Patented Mar. 27, 1934 UNITED STATES PATENT OFFICE Application .lune 24, 1930, Serial No. 463,539

1 Claim.

This invention relates to improvements in electric heating elements and proposes such an element which, although suitable for other purposes, has characteristics which render it particularly desirable for use in electric heaters of the radiant type.

Present day requirements demand that heatters of this type must not only serve their primary purposes of heating but must also be attractive in appearance so as not to detract from the general appearance of the rooms in which they may be placed. It has, therefore, been the practice to utilize concave reflectors in connection with heaters of the radiant type. The reflector of the heater is mounted behind the heating element at such an angle with respect to the ordinary line of vision that the heating element when energized appears to be, not its true size, but the size of the reflector, this being due to the merging of the glowing red element with its image directly behind it in the reflector. In this type of heater, therefore, it is desirable that the heating element glow brightly when in use so as to enhance the appearance of the heater as described.

One object of the invention is to provide a heating element in which the resistance coil and terminals therefor are formed from a single continuous length of wire.

A further object is a heating element which is constructed so that it may be connected to power of a voltage which is available at the place where it is to be installed without the necessity of a transformer and which will be heated to the required brilliancy by current of the voltage available.

A further object is a heating element which, when energized, will be of a uniform brilliance throughout its entire extent.

A still further object is a heating element of the kind generally described in which one of the terminal leads .is formed so that it will not becoine heated to such a degree as to prevent maintenance of a good connection between it and a power terminal.

The invention is illustrated in the accompanying drawing, in which:

Figure l is an elevation of an element constructed in accordance with the invention.

* Figure 2 is an enlarged fragmentary perspec- 1 5 relatively high conductive coating is applied to (Cl. 21B- 19) the central terminal lead to lessen its resistance to the passage of current to the coil.

The element, as illustrated, includes a core 5 upon which the resistance coil 6 is supported. The core 5 is threaded and the wire which forms the coil is wound about the core 5 in the grooves 'l provided by the threads, the said grooves separating adjacent convolutions o1 the coil.

The coil, as shown, is preferably formed from a single continuous wire and during its formation is provided at its ends with integral terminal leads 8 and 9 and centrally with a similar lead l0. in forming the heating coil, the core 5 may be mounted upon a mandrel by which it is rotated during the winding of the resistance wire thereon. in this operation, the terminal lead 8 which is of doubled wire may be rst formed while leaving a free end of such a length that it may be wound about the core 5 toward its left end and after its last turn thereon wound about the doubled length of twisted wire which forms the terminal lead 8 as at 11. From this initial winding on the core, the wire is then tightly wound about the latter toward the opposite end or right end. At the approximate center of the The terminal lead 9 is prefer- 85 turn and a half, the free end of the wire remaining being then wound about the terminal lead 9, as at l2. It is preferred that the terminal leads formed by the double portions of wire be twisted and that all of them when formed lie in the same plane for reasons which will appear hereafter.

In mounting the heating element in the heater casing the said element may be supported by means of the core 5. In connecting the element to power the terminal leads 8 and 9 may be en- 100 ployed or in other instances all three of the terminal leads may be utilized. As pointed out heretofore, it is desirable that the heating coil be heated to bright red in all cases regardless of the voltage of the current. voltage available is 22o volts and the element is connected to power by means of terminal leads 8 and 9 and the resistance coil is heated to glow brightly then when the current voltage is only 110 volts and the same two leads are employed lil) Thus, if the current the resistance coil will glow very dully, if at all. It is the purpose of the lead l0 to overcome this diculty. Assuming, for illustration, that the most prevalent power voltages are 110 and 220, the length of wire between the end terminal leads 8 and 9 is selected so that when the element is connected to power of 220 volts by means of the said leads the resistance coil will glow brightly in the manner desired. When the resistance element is connected to power in this manner both of its halves A and B of the coil are in series. However, if the current Voltage at the place of installation is 110 volts the connection of the halves A and B in this manner would be objectionable for the reason explained. In this case, therefore, the central lead l0 is utilized. The said lead may be connected to one side of the power` line while the end terminal leads 8 and 9 may be connected to the other side of the power line. In this arrangement the halves A and B of the coil are connected in parallel and the entire element glows brilliantly as in the Case where the end terminal leads 8 and 9 were connected to power of 220 volts.

When the central terminal lead 1Q, however, is employed in the manner described, it, or" course, must permit the passage of twice the current that is required by either of the halves A and B of the coil. As a result of this, the lead 10 would, unless otherwise prevented, be heated to such an extent that its consequent corrosion and oxidation would materially impair any connection between it and a power line terminal. In accordance with the invention, therefore, the central terminal lead 10 is coated as at 13 (Figure 3) with a metal of relatively high conductivity such as, for example, silver solder. The coating 13 preferably extends substantially to a point where the two ends or" the wire project from the twisted portion of the lead to follow the grooves in the support 5. When the lead 10 is connected to power after having been coated in this manner the resistance of the said lead is reduced to such an extent that there is substantially no heat produced by the passage of current through it and hence a good connection with a power line terminal can be maintained.

In mounting the element in the heater casing, it is supported by means of the core 5 and the lead 10 is preferably at the back of the element and hence out of sight. The formation of the central lead 10 integral with the resistance coil has the advantage that the latter glows uniformly, when heated, throughout its entire extent regardless of whether the halves A and B of the coil are in series or in parallel and there is no interruption in the arrangement of the adjacent convclutions of the coil.

From the foregoing it will be apparent that a heating element may be constructed in accordance with the invention which will be of the necessary length and which will glow to the extent desired while at the same time it may be connected to sources of power of different voltages. This is of importance from a manufacturing standpoint for the reason that a standardized unit may be formed so that it may be operated in the manner desired upon currents of different voltages and hence meet the requirements of diierent localities.

I claim as my invention:

An electric heating element which is adapted to glow when energized comprising a core, a continuous resistance element wound about said core to provide a heating coil, a terminal lead formed intermediate the ends of said coil as a part of said continuous element, said terminal lead dividing the coil into a plurality of parts adapted to be connected to one side of a power line, a coating of low electrical resistance carried by said terminal lead to prevent it from being heated to an undesirable extent and termina-l leads formed at the opposite ends of said coil as a part of said continuous resistance element whereby said coil parts may be connected to the other side of said power line, the terminal leads at the opposite ends of said coil being in the form of loops and the opposite ends of said element being wound around said loops, said intermediate terminal lead connecting the parts of said coil so that they may be connected to power in series.

ALBERT E. ELLINGER. 

